Alleviation of noxious effects of cattle ranch composts on wheat seed germination by inoculation with Azospirillum spp.

Two commonly-used composts from dairy cow manure that are used to improve poor structure and fertility of desert soils have inhibitory effects on wheat seed germination, probably as a result of their high levels of humic acids. Inoculation of wheat seeds with two species of the plant growth-promoting bacteria Azospirillum brasilense Cd and A. lipoferum JA4 (separately) prior to sowing in these amended soils improved germination, similar to the natural level of germination of seeds in desert soil without compost amendment. Both compost amendments increased height of wheat seedlings in the range of 20–25%, increased shoot dry weight by 15–19%, but severely decreased (51–54% less) root dry weight. Inoculation of wheat seeds with A. brasilense Cd, but not with A. lipoferum JA4, significantly increased plant growth parameters (height, shoot and root dry weight) over control plants grown in soil-compost mixtures. This bacterial species could survive for a period of 20 days in compost humic acid solution, could increase its population when the humic acids served as the sole carbon source, and may change the composition of humic acids in which it grows. We suggest that inoculation with A. brasilense may alleviate noxious effects on germinating seeds caused by compost application by possibly transforming the composition of humic acids in the compost.     

Inoculation of rice with nitrogen-fixing bacteria —problems and perspectives

Summary The present status and merits of inoculating rice with N₂-fixing bacteria are discussed in the light of recent advances. Bacterial inoculation improves plant growth and rice yield but not uniformly. The yield response to inoculation is more pronounced in the presence of moderate levels of fertilizer N. Evidence for the establishment and activity of the inoculated bacteria is limited, and the poor survival of the inoculum under field conditions further complicates the effects of inoculation. There is no clear evidence that improved growth and mineral content following inoculation are due to increased N₂ fixation. Beneficial effects of the inoculum on rice, such as plant growth promotion, N₂ fixation and antagonism effects against pathogens need to be further investigated under laboratory and field conditions. Improved management practices, such as organic amendments, suitable water and soil management, selection of efficient microbial strains, selection of effective breeding lines with high associative nitrogen fixation, and better management of agrochemicals are some of the measures suggested for deriving benefits from bacterial associations with rice.     

Increased emergence of spring wheat after inoculation with Pseudomonas chlororaphis isolate 2E3 under field and laboratory conditions

Inoculation at the time of planting with Pseudomonas chlororaphis strain 2E3 increased the emergence of spring wheat by 8% and 6% at two different sites in northern Utah. Isolate 2E3 strongly inhibited the growth of the wheat pathogen Fusarium culmorum on artificial media. A second isolate of P. chlororaphis (strain O6) also inhibited fungal growth on artifical media but did not increase emergence of the spring wheat at the same field sites. Inoculation of winter wheat by 2E3 did not promote emergence when planted into field soil sterilized by fumigation with methyl bromide. Under laboratory conditions, emergence of spring wheat in sterilized soils from both sites was at least 90%. In the soils that were not sterilized, emergence was below 25% in soil from one site and below 50% in soil from the other. Treating seeds with 2E3 significantly improved emergence in a sterile soil-containing matrix that had been inoculated with the wheat pathogen Fusarium culmorum. Consequently, we propose that increases in wheat emergence can be attributed to the suppression by 2E3 of pathogenic organisms present in the native field soils. A strain of Rhizoctonia solani, shown to the pathogenic on winter wheat, was isolated from one of these soils.     

Molecular characterization and PCR detection of a nitrogen-fixing Pseudomonas strain promoting rice growth

Nitrogen-fixing plant growth-promoting rhizobacteria (PGPR) from the genus Pseudomonas have received little attention so far. In the present study, a nitrogen-fixing phytohormone-producing bacterial isolate from kallar grass (strain K1) was identified as Pseudomonas sp. by rrs (16S ribosomal RNA gene) sequence analysis. rrs identity level was high with an uncharacterized marine bacterium (99%), Pseudomonas sp. PCP2 (98%), uncultured bacteria (98%), and Pseudomonas alcaligenes (97%). Partial nifH gene amplified from strain K1 showed 93% and 91% sequence similarities to those of Azotobacter chroococcum and Pseudomonas stutzeri, respectively. The effect of Pseudomonas strain K1 on rice varieties Super Basmati and Basmati 385 was compared with those of three non-Pseudomonas nitrogen-fixing PGPR (Azospirillum brasilense strain Wb3, Azospirillum lipoferum strain N4 and Zoogloea strain Ky1) used as single-strain inoculants. Pseudomonas sp. K1 was detected in the rhizosphere of inoculated plants by enrichment culture in nitrogen-free growth medium, which was followed by observation under the microscope as well as by PCR using a rrs-specific primer. For both rice varieties, an increase in shoot biomass and/or grain yield over that of noninoculated control plants was recorded in each inoculated treatment. The effect of Pseudomonas strain K1 on grain yield was comparable to those of A. brasilense Wb3 and Zoogloea sp. Ky1 for both rice varieties. These results show that nitrogen-fixing pseudomonads deserve attention as potential PGPR inoculants for rice.     

Influence of a plant growth-promoting pseudomonad and vesicular-arbuscular mycorrhizal fungus on alfalfa and birdsfoot trefoil growth and nodulation

Summary In a growth chamber study we examined the influence of a plant growth-promoting rhizobacterium, Pseudomonas putida R-20, and an acid-tolerant vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus intraradices 25, on Medicago sativa L. and Lotus corniculatus L. growth and nodule development. Seedlings were planted in an acidic (pH 5.5), P-deficient soil containing re-established native microflora (minus VAM) and appropriate rhizobia, and inoculated with the rhizobacterium, the VAM fungus, or both. The plants were assayed at three intervals for up to 10–11 weeks. The growth-promoting rhizobacteria alone increased alfalfa shoot mass by 23% compared to all other treatments, but only at 8 weeks of growth, apparently by promoting nodulation and N₂ fixation (acetylene reduction activity). The presence of VAM, either alone or in combination with the rhizobacteria, generally decreased root length but only at 8 weeks also. As a group, the inoculation treatments increased all nodular measurements by 10 weeks of growth. Few treatment effects were found at 7 and 9 weeks for birdsfoot trefoil; neither plant nor nodular measurements differed among treatments. By 11 weeks, shoot mass was increased by the rhizobacteria alone by 36% compared to the control. As a group, the inoculation treatments all showed increased nodular responses by this time. The rhizobacteria stimulated mycorrhizal development on both plant species, but only at the initial samplings. No synergistic effects between the plant growth-promoting rhizobacterium and VAM inoculation were found. Although these results lend credence to the concept of managing microorganisms in the rhizosphere to improve plant growth, they emphasize the necessity for a more thorough understanding of microbial interactions as plants mature.     

Seed inoculation with <Emphasis Type="Italic">Bacillus</Emphasis> spp. improves seedling vigour in oil-seed plant <Emphasis Type="Italic">Jatropha curcas</Emphasis> L.

Jatropha (Jatropha curcas L.) is a non-edible oil-seed plant with adaptability to marginal semi-arid lands and wastelands. The Indian Government is promoting jatropha to reduce dependence on the crude oil and to achieve energy independence by the year 2012, under the National Biodiesel Mission. Selected strains of Bacillus spp., either supplemented with or without chitin, were tested for their ability to promote growth of jatropha seedlings in pot culture studies. The strains supported growth of jatropha seedlings up to 42 days after sowing. Among all strains, Bacillus pumilus (IM-3) supplemented with chitin showed over all plant growth promotion effect resulting in enhanced shoot length (113%), dry shoot mass (360%), dry root mass (467%), dry total plant mass (346%), leaf area (256%), and chlorophyll content (74%) over control. Treating seeds with strain IM-3 without chitin resulted in enhanced dry shoot mass (473%), dry total plant mass (407%), and chlorophyll content (82%). However, Bacillus polymyxa (KRU-22) with chitin supported maximum root length (143%). Either strain IM-3 alone or in combination with other promising strains could be promoted further for enhanced initial seedling growth of jatropha.     

西瓜根际促生菌筛选及生物育苗基质研制

通过从西瓜根际分离筛选具根际定殖能力的植物根际促生菌,将其保活添加至普通育苗基质研制生物育苗基质,以确保功能菌株能够在苗期定殖根际,进而在移栽后发挥促生功能。结果表明,分离获得一株同时具有产吲哚乙酸(IAA)和NH_3,且对尖孢镰刀菌和茄科劳尔氏菌均有拮抗作用的植物根际促生菌(PGPR)菌株N23;在三季育苗试验中,与普通基质处理(CK)相比,添加菌株N23的生物育苗基质所育种苗,在多项苗期生长指标上均表现出稳定的促生作用;盆栽试验表明,除叶绿素相对含量测量值(SPAD)外,生物基质所育西瓜种苗的其他检测指标均显著高于对照(普通育苗基质所育种苗,下同);田间试验表明,生物基质所育种苗西瓜、黄瓜、辣椒和番茄种苗移苗后,在苗期植株株高和茎粗均显著优于对照,在产量上均增产10%以上。结合形态、生理生化特征和16S rDNA基因序列分析,初步鉴定菌株N23为芽孢杆菌属细菌(Bacillus sp.)。综上,利用芽孢杆菌N23研制的生物育苗基质能够有效促进所育不同作物种苗质量,增强移栽后作物的生长和田间产量。因此,本研究能够为根际有益微生物的应用提供新的思路,为生物育苗基质的研制提供理论支撑。     

Selection of efficient vesicular-arbuscular mycorrhizal fungi for wetland rice (Oryza sativa L.)

Summary We tested the response of the wetland rice cultivar Prakash to inoculation with ten vescular-arbucular mycorrhizal (VAM) fungi (three selected from the first screening and seven isolated from local paddy fields) in a pot experiment under flooded conditions in order to select the most efficient mycorrhizal fungi to inoculate the rice nursery. A sandy clay loam soil was used as the substrate, fertilized with the recommended N and K levels (100 kg N ha^–1 as ammonium sulphate and 50 kg K ha^–1 as muriate of potash) and half the recommended level of P (25 kg ha^–1 as super phosphate). The inoculation was made into dry nursery beds and the beds were flooded when the seedlings were about 25 cm high, in 15 days. Twenty-eight-day old seedlings were transferred to pots filled with well puddled soil flooded with 5 cm of standing water. Based on the increase in grain yield and total biomass, Glomus intraradices and Acaulospora sp. were considered efficient and suitable for inoculation into rice nurseries.     

Orientation behaviour of earthworms (Lumbricidae) towards different crops

Summary In an outdoor experiment the distribution of earthworms (Lumbricus spp., Allolobophora spp.) under different plant species was studied. Earthworms avoid uncovered areas, but show different reactions under vegetation. This effect reappears in the same manner every year. A particular preference was shown for clover whereas onion was least preferred. Possible reasons for this behaviour are the extent of covering, the moisture regime and exudates of the plants. According to the results obtained the deciding factor seems to be the extent of cover whereas odorous substances are of secondary importance.Dedicated to the late Prof. Dr. M.S. Ghilarov     

Influence of host seed on metabolic activity of Enterobacter cloacae in the spermosphere

Little is known regarding the influences of nutrients released from plants on the metabolic activity of colonizing microbes. To gain a better understanding of these influences, we used bioluminescence- and oxygen consumption-based methods to compare bacterial metabolic activity expressed during colonization of two different seed types. Metabolic activity expressed by Enterobacter cloacae during colonization of pea seeds, which exude high levels of reduced carbon nutrients, was compared with that during colonization of cucumber seeds, which exude orders of magnitude less reduced carbon nutrients. Metabolic activity levels expressed by E. cloacae populations were much higher throughout a 72 h colonization period on pea seed compared with those observed on cucumber seed, directly correlating metabolic activity level with amounts of nutrients released by seeds. In vitro studies indicated E. cloacae cells expressed different levels of metabolic activity when incubated with different individual carbohydrates commonly found in cucumber and pea seed exudates. The addition of exogenous carbohydrate to cucumber seed increased metabolic activity expressed by colonizing E. cloacae; with the level of increase dependent on both quantity and type of carbohydrate supplement. Subtraction of carbohydrate available to E. cloacae on cucumber and pea seeds through mutation in pfkA decreased metabolic activity by this bacterium. Results presented here provide strong evidence that metabolic activity of spermosphere-colonizing bacteria is host dependent, and that levels of activity are based largely on both quantitative and qualitative composition of host exudate released during seed germination.     

Maize genotype effects on the response to Azospirillum inoculation

Two field experiments were carried out in Northern Argentina, during the 1989–1990 and 1990–1991 growing seasons, on Argentinian and Brazilian maize genotypes. The inoculant consisted of a mixture of four Azospirillum brasilense strain isolated from surface-sterilized maize roots in Argentina and three A. lipoferum strains isolated from surface-sterilized maize or sorghum roots in Brazil. Establishment of the inoculated strains was confirmed by the antibiotic resistance of the strains in the highest dilution vials. In all treatments, numbers of Azospirillum spp. were increased and the inoculated strains were found in the highest dilutions. While grain yields of the different genotypes varied between 1700 and 7300 kg ha^-1, total N accumulation was much less variable. Significant inoculation effects on total N accumulation and on grain yields were consistently negative with one Argentinian genotype and positive with four Argentinian and two Brazilian genotypes. Significant inoculation effects on leaf nitrate reductase activity at the flowering stage, observed in the range-55% to +176%, indicated the presence of various interactions between the plant NO _inf3 ^sup- metabolism and Azospirillum spp. Three Brazilian and one Argentinian maize genotype showed significant decreases in leaf nitrate reductase due to inoculation while four Argentinian genotypes showed significant increases in leaf nitrate reductase activity. The results of the present study, were consistent over the two field experiments and strongly indicate that more detailed plant genotype-Azospirillum spp. strain interaction studies, taking the entire N metabolism in the plant into account, are needed to allow better inoculation results of cereal crops.     

Responses of native legume desert trees used for reforestation in the Sonoran Desert to plant growth-promoting microorganisms in screen house

Three slow-growing legume trees used for desert reforestation and urban gardening in the Sonoran Desert of Northwestern Mexico and the Southwestern USA were evaluated whether their growth can be promoted by inoculation with plant growth-promoting bacteria (Azospirillum brasilense and Bacillus pumilus), unidentified arbuscular mycorrhizal (AM) fungi (mainly Glomus sp.), and supplementation with common compost under regular screenhouse cultivation common to these trees in nurseries. Mesquite amargo (Prosopis articulata) and yellow palo verde (Parkinsonia microphylla) had different positive responses to several of the parameters tested while blue palo verde (Parkinsonia florida) did not respond. Survival of all tree species was over 80% and survival of mesquite was almost 100% after 10 months of cultivation. Inoculation with growth-promoting microorganisms induced significant effects on the leaf gas exchange of these trees, measured as transpiration and diffusive resistance, when these trees were cultivated without water restrictions.     

接种bradyrhizobium sp.对豇豆生物量及根瘤的影响

Vigna unguiculata(L.)Walp (cowpea)is a tropical legume of very high nutrive and economic values.A laboratory experiment.was conducted to evaluate the BNF (biological nitrogen fixation) effciency of 4 strains of Bradyrhizobium sp.(VUXYI,VUIE1,VUMDS1 and VUID1).From the results obtained these strains were classified into efficiency groups,with VUID1 being the most efficient and VUXY1 the least efficient.the effect of inoculation was tested on 2 cowpea varieties in a field experiment.Remarkable increases in nodulation biomass and crop yield were observed.An increase from 58% ti 81% in dry seed was obtained for the two varieties.A significance test revealed a signifecantly positive correlation between nodulation and biomass.     

Oligotrophic pseudomonads in the rhizosphere: Suppressiveness to Pythium damping-off of cucumber seedlings (Cucumis sativus L.)

Summary Pseudomonads recovered from the cucumber rhizosphere were evaluated for their ability to suppress Pythium ultimum damping-off. Full-strength and 250-fold diluted selective media formulations with King's B medium (KB and KB/250, respectively) as the basal medium were used as the recovery media. Eight per cent of the isolates recovered (11/138) could induce suppression to Pythium damping-off and 45% of these biocontrol agents produced fluorescent pigments. No differences in the ability to induce suppression among the isolates recovered on full-strength and diluted media were detected. The growth rates of the selected isolates indicated that growth in KB broth was faster or equal to that in KB/10. Therefore, no obligate oligotrophs were recovered. Additionally, growth was observed in 15 000-fold diluted KB for 10 of 11 test isolates, which indicated that these isolates were facultative oligotrophs. In general, the faster growing isolates were more likely to induce suppression when used as seed treatments. Finally, the in vitro antifungal properties of test isolates against P. ultimum indicated that 4 of the 11 isolates inhibited P. ultimum.     

Influence of sewage sludge and heavy metals on nematodes in an arable soil

Summary The abundance of nematodes was investigated in agricultural plots treated in three different ways, the first with no treatment, the second with 300 m³ ha^-1 a^-1 raw sewage sludge and the third with 300 m³ ha^-1 a^-1 sewage sludge with the addition of heavy metals. The nematodes were determined down to the genus and were assigned to five feeding groups. Total nematode numbers were highest in the site treated with sewage sludge and heavy metals. The smallest total numbers were found in the control site. The plant-feeding nematode genera showed different patterns of abundance depending on the sludge treatment and heavy metal content. For the mycophagic and bacteriophagic nematodes, numbers increased with the amount of sludge, especially in the sites with a higher heavy metal content. The family Rhabditidae was the most numerous group in the sludge plus heavy metals treatment. In contrast to these findings, the omnivorous nematodes were very rare in the sludgetreated plots and were completely absent in plots treated with sludge plus heavy metals, whereas predatory nematodes were numerous only after the application of sludge alone.     

微生物介导的农业土壤氧化亚氮减排研究进展

氧化亚氮(N₂O)是一种在大气存留时间长且破坏臭氧层的重要温室气体。农业土壤源N₂O是其重要来源,具有产生路径广、影响因素多、调控复杂等特点。减少农业土壤N₂O排放一直是研究的热点。含有N₂O还原酶的N₂O还原细菌能将N₂O还原为氮气(N2),这是目前已知的微生物还原N₂O唯一的汇。直接应用微生物减少农业土壤N₂O排放是一种新兴的减排技术。本文详细阐述了农业土壤N₂O的生物源与汇,重点论述了N₂O减排微生物的筛选及应用策略。综述了微生物介导的农业土壤N₂O减排的两种微生物生态学机制：一种是利用含有nos Z基因的N₂O还原细菌直接减少N₂O排放,另一种是利用能改变N₂O还原细菌群落组成和丰度及其活性的植物根际促生菌间接减少N₂O排放。最后,讨论了影响微生物介导的...